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Discussion Starter #1
I purchased a 65 mustang (my first mustang) a few weeks ago. It has the original 289 with a 347 stroker kit, electronic ignition, electric fan for radiator, other than that pretty much stock.

Since I purchased the car has died on me a few times while driving and I’m trying to get to the bottom of it.

I first started by replacing the batter, as it was tested at advanced and they told me it was bad. It dies again.

I then replace the alternator, dies again. Change the voltage regulator. Still dying.

The factory voltage regulator was taken out of the car and replaced with a Tuff Stuff Performance Replacement Alternator Regulators 7530A. It bolts directly to the back of the alternator to eliminate the wiring harness.

I had the new motor craft 7078 65 amp alternator tested to ensure it wasn’t bad. Also had the old one tested which did test bad. It also tested the voltage regulator and it passed as well. I attached a photo of the old alternator and voltage regulator. The new ones are identical.

So I have a new batter, alternator, and voltage regulator yet the charging system does not seem to be doing anything.

If I put my leads across the batter while the engine is on I get about 12.3 volts, revving the engine doesn’t fluctuate the reading at all. From bat terminal to grnd terminal on the alternator while running, no voltage is read at all. Same with the field terminal to ground. From the positive battery terminal to ground terminal on alternator I get that same 12.3 volts while the engine is running.

The grounds are as follows
1. 4 gauge wire from negative battery post to top alternator mounting bolt.
2. Braided steel ground from head to firewall.
3. 10 gauge Ground from alternator terminal to chassis.
4. 10 gauge ground from chassis to negative battery post.

I have tried everything I can think of and still cannot seem to get a reading on my leads above 12.3 volts. Any and all help would be very much appreciated!
 

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do you have a schematic of the charging circuit?

How it knows to charge?

It sounds like it is not correctly wired

Do you have any literature about your specific alternator?
 

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Discussion Starter #3
Thanks for the response!

I don’t have a schematic unfortunately because the previous owner made these changes, that’s part of my struggle.

It is a motorcraft 7078. It’s pretty straight forward and set up identical to an original alternator. It has a ground, field, starter, and battery post on the rear side.

It tests fine at an auto shop, shows the voltage regulator and alternator work fine as wired. The only line that goes to the alternator different then on a bench alternator tester is the cable going from the positive battery post to the battery post on the back of the alternator. That is the only difference at all between the bench tester and in the car.

I’ve even added 2 additional grounds. I added one from the ground terminal on the alternator to the chassis and one from the negative battery terminal to the chassis with no luck.
 

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full field it then

it must be missing an input
without a diagram, its guessing
 

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there should be a test screw on the reg

in order to troubleshoot this you must know how its supposed to work

i suggest you look up how alternators work, they are basically all the same
 

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Discussion Starter #7
Indy, as I think I mentioned it’s an aftermarket voltage regulator that mounts directly to the back of the alternator. I think I’ve got a pretty good handle on how the alt works. The VR is a Tuff Stuff Performance Replacement Alternator Regulators 7530A.

Now today I ran a wire directly from the field post on the alt to the positive terminal on the battery and was getting a charge, reving to 1500 rpm I was getting over 15 volts so I shut it down. I’m not entirely sure what that tells me other than I bypassed the VR by doing this?
 

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since you know how an alternator works


tell me what you are missing?

i say you dont
 

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Discussion Starter #9
Indy seems like you in here more to try and doubt knowledge I have vs trying to be helpful.

I did get it resolved. Despite the alternator testing positive at now 3 separate locations on bench testers, I purchased a new alternator again. Put the new alternator in and worked right away.

So the cause of all my headaches was a a bad alternator out of the box that somehow would test positive on bench testers. Case closed.
 

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Indy seems like you in here more to try and doubt knowledge I have vs trying to be helpful.

I did get it resolved. Despite the alternator testing positive at now 3 separate locations on bench testers, I purchased a new alternator again. Put the new alternator in and worked right away.

So the cause of all my headaches was a a bad alternator out of the box that somehow would test positive on bench testers. Case closed.
Wow, so 3 places tested the alt and it tested out fine? Same thing happens to batteries often. They’ll test out fine, but just don’t work. I guess throwing parts at the problem worked out this time!! Sometimes you just gotta load the parts cannon I guess.
 

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Indy seems like you in here more to try and doubt knowledge I have vs trying to be helpful.

I did get it resolved. Despite the alternator testing positive at now 3 separate locations on bench testers, I purchased a new alternator again. Put the new alternator in and worked right away.

So the cause of all my headaches was a a bad alternator out of the box that somehow would test positive on bench testers. Case closed.
you took your alt to get diagnosed, so i dont have to doubt your knowledge, you admitted yourself

you had a chance to 'bench test' it on your car, and learn how it works

I asked you to full field it.....you chose not to

was your choice, so dont get butt hurt about it.
 

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Wow, so 3 places tested the alt and it tested out fine? Same thing happens to batteries often. They’ll test out fine, but just don’t work. I guess throwing parts at the problem worked out this time!! Sometimes you just gotta load the parts cannon I guess.
if diagnosed, no, the parts cannon does not need to be triggered
 

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Wow, so 3 places tested the alt and it tested out fine? Same thing happens to batteries often. They’ll test out fine, but just don’t work. I guess throwing parts at the problem worked out this time!! Sometimes you just gotta load the parts cannon I guess.
if diagnosed, no, the parts cannon does not need to be triggered
Indy, you love when the parts cannon gets loaded!
I agree though, a proper diagnosis will save you tons. But, how about this situation? In this case, it worked.
 

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in this case?

i see no difference, the poster didn't want to diagnose, wanted someone else to

got a bad diagnosis, and defaulted to the cannon

no different than any other stranger telling you to change parts rather than yourself telling yourself

if the poster paid for the bad diagnosis, hopefully they got their money back

wanna work on your own car........might be a good idea to learn how to diagnose
 
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